Method of material processing by laser filamentation

ABSTRACT

A method is provided for the internal processing of a transparent substrate in preparation for a cleaving step. The substrate is irradiated with a focused laser beam that is comprised of pulses having an energy and pulse duration selected to produce a filament within the substrate. The substrate is translated relative to the laser beam to irradiate the substrate and produce an additional filament at one or more additional locations. The resulting filaments form an array defining an internally scribed path for cleaving said substrate. Laser beam parameters may be varied to adjust the filament length and position, and to optionally introduce V-channels or grooves, rendering bevels to the laser-cleaved edges. Preferably, the laser pulses are delivered in a burst train for lowering the energy threshold for filament formation, increasing the filament length, thermally annealing of the filament modification zone to minimize collateral damage, improving process reproducibility, and increasing the processing speed compared with the use of low repetition rate lasers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/363,568, titled “Method of Material Processing by LaserFilamentation” and filed on Jul. 12, 2010, the entire contents of whichare incorporated herein by reference, and to U.S. ProvisionalApplication No. 61/372,967, titled “Method of Material Processing byLaser Filamentation” and filed on Aug. 12, 2010, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

The present disclosure is related to methods of laser processing ofmaterials. More particularly, the present disclosure is related tomethods of singulation and/or cleaving of wafers, substrates, andplates.

In current manufacturing, the singulation, dicing, scribing, cleaving,cutting, and facet treatment of wafers or glass panels is a criticalprocessing step that typically relies on diamond cutting, with speeds of30 cm/sec for flat panel display as an example. After diamond cutting, amechanical roller applies stress to propagate cracks that cleave thesample. This process creates poor quality edges, microcracks, wide kerfwidth, and substantial debris that are major disadvantages in thelifetime, quality, and reliability of the product, while also incurringadditional cleaning and polishing steps. The cost of de-ionized water torun the diamond scribers are more than the cost of ownership of thescriber and the technique is not environmentally friendly since watergets contaminated and needs refining that itself adds the costs. Byadvance techniques dyes on the wafers are getting smaller and closer toeach other that limit the diamond scribing. 30 um is a good scribingwidth and 15 um is challenging. Since diamond scribing uses mechanicalforce to scribe the substrate, thin samples are very difficult toscribe. The FPD industry is seeking to reduce glass thicknesses to150-300 um from conventional 400-700 um that is used currently andscribing the plates is the major issue. Indeed the FPD industry islooking to use thin tempered glass instead of ordinary glass fordurability.

Laser ablative machining is an active development area for singulation,dicing, scribing, cleaving, cutting, and facet treatment, but hasdisadvantages, particularly in transparent materials, such as slowprocessing speed, generation of cracks, contamination by ablationdebris, and moderated sized kerf width. Further, thermal transportduring the laser interaction can lead to large regions of collateralthermal damage (i.e. heat affected zone). Laser ablation processes canbe dramatically improved by selecting lasers with wavelengths that arestrongly absorbed by the medium (for example, deep UV excimer lasers orfar-infrared CO2 laser). However, the above disadvantages cannot beeliminated due to the aggressive interactions inherent in this physicalablation process.

Alternatively, laser ablation can also be improved at the surface oftransparent media by reducing the duration of the laser pulse. This isespecially advantageous for lasers that are transparent inside theprocessing medium. When focused onto or inside transparent materials,the high laser intensity induces nonlinear absorption effects to providea dynamic opacity that can be controlled to accurately depositappropriate laser energy into a small volume of the material as definedby the focal volume. The short duration of the pulse offers severalfurther advantages over longer duration laser pulses such as eliminatingplasma reflections and reducing collateral damage through the smallcomponent of thermal diffusion and other heat transport effects duringthe much shorter time scale of such laser pulses. Femtosecond andpicosecond laser ablation therefore offer significant benefits inmachining of both opaque and transparent materials. However, machiningof transparent materials with pulses even as short as tens to hundredsof femtosecond is also associated with the formation of rough surfacesand microcracks in the vicinity of laser-formed hole or trench that isespecially problematic for brittle materials like glasses and opticalcrystals. Further, ablation debris will contaminate the nearby sampleand surrounding surfaces.

A kerf-free method of cutting or scribing glass and related materialsrelies on a combination of laser heating and cooling, for example, witha CO2 laser and a water jet. [U.S. Pat. No. 5,609,284 (Kondratenko);U.S. Pat. No. 6,787,732 UV laser (Xuan)] Under appropriate conditions ofheating and cooling in close proximity, high tensile stresses aregenerated that induces cracks deep into the material, that can bepropagated in flexible curvilinear paths by simply scanning thelaser-cooling sources across the surface. In this way, thermal-stressinduced scribing provides a clean splitting of the material without thedisadvantages of a mechanical scribe or diamond saw, and with nocomponent of laser ablation to generate debris. However, the methodrelies on stress-induced crack formation to direct the scribe andrequires [WO/2001/032571 LASER DRIVEN GLASS CUT-INITIATION] a mechanicalor laser means to initiate the crack formation. Short duration laserpulses generally offer the benefit of being able to propagateefficiently inside transparent materials, and locally inducemodification inside the bulk by nonlinear absorption processes at thefocal position of a lens. However, the propagation of ultrafast laserpulses (>˜5 MW peak power) in transparent optical media is complicatedby the strong reshaping of the spatial and temporal profile of the laserpulse through a combined action of linear and nonlinear effects such asgroup-velocity dispersion (GVD), linear diffraction, self-phasemodulation (SPM), self-focusing, multiphoton/tunnel ionization (MPI/TI)of electrons from the valence band to the conduction band, plasmadefocusing, and self-steepening [S L Chin et al. Canadian Journal ofPhysics, 83, 863-905 (2005)]. These effects play out to varying degreesthat depend on the laser parameters, material nonlinear properties, andthe focusing condition into the material.

Kamata et al. [SPIE Proceedings 6881-46, High-speed scribing offlat-panel display glasses by use of a 100-kHz, 10-W femtosecond laser,M. Kamata, T. Imahoko, N. Inoue, T. Sumiyoshi, H. Sekita, Cyber LaserInc. (Japan); M. Obara, Keio Univ. (Japan)] describe a high speedscribing technique for flat panel display (FPD) glasses. A 100-kHzTi:sapphire chirped-pulse-amplified laser of frequency-doubled 780 nm,300 fs, 100 μJ output was focused into the vicinity of the rear surfaceof a glass substrate to exceed the glass damage threshold, and generatevoids by optical breakdown of the material. The voids reach the backsurface due to the high repetition rate of the laser. The connectedvoids produce internal stresses and damage as well as surface ablationthat facilitate dicing by mechanical stress or thermal shock in adirection along the laser scribe line. While this method potentiallyoffers fast scribe speeds of 300 mm/s, there exists a finite kerf width,surface damage, facet roughness, and ablation debris as the internallyformed voids reach the surface.

SUMMARY

In a first embodiment, there is provided a method of preparing asubstrate for cleavage, the method comprising the steps of: irradiatingthe substrate with one or more pulses of a focused laser beam, whereinthe substrate is transparent to the laser beam, and wherein the one ormore of pulses have an energy and pulse duration selected to produce afilament within the substrate; translating the substrate relative to thefocused laser beam to irradiate the substrate and produce an additionalfilament at one or more additional locations; wherein the filamentscomprise an array defining an internally scribed path for cleaving thesubstrate. The method preferably includes the step of cleaving thesubstrate.

The substrate is preferably translated relative to the focused laserbeam with a rate selected to produce a filament spacing on a micronscale. Properties of the one or more laser pulses are preferablyselected to provide a sufficient beam intensity within the substrate tocause self-focusing of the laser beam.

The one or more pulses may be provided two or more times with aprescribed frequency, and the substrate may be translated relative tothe focused laser beam with a substantially constant rate, thusproviding a constant spacing of filaments in the array.

The one or more pulses include a single pulse or a train of two or morepulses. Preferably, a time delay between successive pulses in the pulsetrain is less than a time duration over which relaxation of one or morematerial modification dynamics occurs. A pulse duration of each of theone or more pulses is preferably less than about 100 ps, and morepreferably less than about 10 ps.

A location of a beam focus of the focused laser beam may be selected togenerate the filaments within the substrate, wherein at least onesurface of the substrate is substantially free from ablation. A locationof a beam focus of the focused laser beam may be selected to generate aV groove within at least one surface of the substrate.

The substrate may be a glass or a semiconductor and may be selected fromthe group consisting of transparent ceramics, polymers, transparentconductors, wide bandgap glasses, crystals, crystal quartz, diamond, andsapphire.

The substrate may comprise two or more layers, and wherein a location ofa beam focus of the focused laser beam is selected to generate filamentswithin at least one of the two or more layers. The multilayer substratemay comprise multi-layer flat panel display glass, such as a liquidcrystal display (LCD), flat panel display (FPD), and organic lightemitting display (OLED). The substrate may also be selected from thegroup consisting of autoglass, tubing, windows, biochips, opticalsensors, planar lightwave circuits, optical fibers, drinking glass ware,art glass, silicon, III-V semiconductors, microelectronic chips, memorychips, sensor chips, light emitting diodes (LED), laser diodes (LD), andvertical cavity surface emitting laser (VCSEL).

A location of a beam focus of the focused laser beam may be selected togenerate filaments within two or more of the two or more layers, whereinthe focused laser beam generates a filament in one layer, propagatesinto at least one additional layer, and generates a filament is the atleast one additional layer.

Alternatively, the location of a beam focus of the focused laser beammay be first selected to generate filaments within a first layer of thetwo or more layers, and the method may further comprise the steps of:positioning a second beam focus within a second layer of the two or morelayers; irradiating the second layer and translating the substrate toproduce a second array defining a second internally scribed path forcleaving the substrate. The substrate may be irradiated from an oppositeside relative to when irradiating the first layer. Furthermore, prior toirradiating the second layer, a position of the second beam focus may belaterally translated relative a position of the beam focus whenirradiating the first layer. A second focused laser beam may be used toirradiate the second layer.

A further understanding of the functional and advantageous aspects ofthe disclosure can be realized by reference to the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure will now be described, by way of exampleonly, with reference to the drawings, in which:

FIG. 1 presents (a) front and (b) side views of the laser filamentationscribing arrangement for scribing transparent materials.

FIG. 2 presents a front view of (a) laser filamentation with V groovescribing of transparent substrate and (b) V groove scribing withsuppressed filament formation.

FIG. 3 illustrates laser scribing of transparent material with internalfilament formation with V groove formation on the top and bottom surfaceapplying reflective element with focusing arrangement.

FIG. 4 shows laser scribing using two focusing apparatus applied fromtop and bottom surface.

FIG. 5 presents a side view of a scribed substrate, where the top,bottom or both edges can be chamfered.

FIG. 6 presents a focusing arrangement of delivering multiple converginglaser beams for creating multiple filaments simultaneously in atransparent substrate at different physical positions, directions,angles, and depths, such that the filaments are overlapping to enablethe single-step cleaving of beveled facets or other facet shapes.

FIG. 7 presents three different focusing arrangements for laserfilamentation scribing (a) a top transparent substrate without damagingtop surface of a bottom substrate, (b) the bottom substrate from a toplocation, and (c) a double plate assembly which can be scribedseparated, or laser scribed simultaneously, forming filaments in bothsubstrates without optical breakdown in the medium between the plates sothat the double plate assembly can be separated along similarcurvilinear or straight lines.

FIG. 8 illustrates laser scribing of a double layer apparatus includingtwo transparent substrates using two focusing beams. Each focus can beadjusted to form a filament, V groove or a combination thereof.

FIG. 9 provides top and side views of a double layer glass afterscribing where (a) only internal filaments are formed, (b) internalfilaments and top surface V grooves are formed, and (c) only a V grooveis formed on the top surfaces of both plates.

FIG. 10 illustrates scribing laminated glass from top and bottom sidewith and without offset.

FIG. 11 illustrates a method of laser bursts filament scribing of stacksof very thin substrates.

FIG. 12 is an optical microscope image of a glass plate viewed through apolished facet prior to mechanical cleaving, showing laser filamentationtracks formed under identical laser exposure with laser focusing by thelens positioned near the lower (a), middle (b) and top (c) regions ofthe glass plate.

FIG. 13 shows a microscope image of glass imaged at the top (a) andbottom (b) surfaces prior to mechanical cleaving, with a track of laserfilaments written inside the bulk glass.

FIG. 14 shows facet edge views of glass plates after mechanical cleavingin which a track of laser filaments was formed at moderate (a) and fast(b) scanning speed during the laser exposure.

FIG. 15 shows facet edge microscope views comparing the lasermodification in 1 mm thick glass formed with an identical number ofequal-energy laser pulses applied at (a) low repetition rate, (b) and insingle pulse high energy low repetition rate pulse trains. Single pulsehas energy of all pulses in one burst train.

FIG. 16 provides microscope images of scribed glass applying V grooveand filament with high repetition rate laser, showing: (a) side view,(b) top view and (c) front view.

FIG. 17 is a front view of three different V groove formation using highrepetition rate laser.

FIG. 18 provides an image showing the scribing of flat panel displayglass. Two laminated glass with 400 um thickness are scribedsimultaneously; a) side view and b) front view.

DETAILED DESCRIPTION

Various embodiments and aspects of the disclosure will be described withreference to details discussed below. The following description anddrawings are illustrative of the disclosure and are not to be construedas limiting the disclosure. Numerous specific details are described toprovide a thorough understanding of various embodiments of the presentdisclosure. However, in certain instances, well-known or conventionaldetails are not described in order to provide a concise discussion ofembodiments of the present disclosure.

As used herein, the terms, “comprises” and “comprising” are to beconstrued as being inclusive and open ended, and not exclusive.Specifically, when used in the specification and claims, the terms,“comprises” and “comprising” and variations thereof mean the specifiedfeatures, steps or components are included. These terms are not to beinterpreted to exclude the presence of other features, steps orcomponents.

As used herein, the term “exemplary” means “serving as an example,instance, or illustration,” and should not be construed as preferred oradvantageous over other configurations disclosed herein.

As used herein, the terms “about” and “approximately”, when used inconjunction with ranges of dimensions of particles, compositions ofmixtures or other physical properties or characteristics, are meant tocover slight variations that may exist in the upper and lower limits ofthe ranges of dimensions so as to not exclude embodiments where onaverage most of the dimensions are satisfied but where statisticallydimensions may exist outside this region. It is not the intention toexclude embodiments such as these from the present disclosure.

As used herein, the term “transparent” means a material that is at leastpartially transparent to an incident optical beam. More preferably, atransparent substrate is characterized by absorption depth that issufficiently large to support the generation of an internal filament byan incident beam according to embodiments described below.

FIG. 1 presents a schematic arrangement shown in (a) front and (b) sideviews for forming laser filaments in a transparent substrate. Shortduration laser pulses 10 are focused with objective lens 12 insidetransparent substrate 14. At appropriate laser pulse energy, the laserpulse, or sequence of pulses, or burst-train of pulses, a laser filament18 is generated within the substrate, producing internal microstructuralmodification with a shape defined by the laser filament volume. Bymoving the sample relative to the laser beam during pulsed laserexposure, a continuous trace of filament tracks 20 are permanentlyinscribed into the glass volume as defined by the curvilinear orstraight path followed by the laser in the sample.

Without intending to be limited by theory, it is believed that thefilaments are produced by weak focusing, high intensity short durationlaser light, which can self-focus by the nonlinear Kerr effect, thusforming a so-called filament. This high spatio-temporal localization ofthe light field can deposit laser energy in a long narrow channel, whilealso being associated with other complex nonlinear propagation effectssuch as white light generation and formation of dynamic ring radiationstructures surrounding this localized radiation.

On the simplest level, the filamentation process is believed to dependmainly on two competing processes. First, the spatial intensity profileof the laser pulse acts like a focusing lens due to the nonlinearoptical Kerr effect. This causes the beam to self-focus, resulting in anincrease of the peak intensity. This effect is limited and balanced byincreasing diffraction as the diameter decreases until a stable beamwaist diameter is reached that can propagate distances many times longerthan that expected from a simple calculation of the confocal beamparameter (or depth of focus) from this spot size.

At high peak intensity, multiphoton ionization, field ionization, andelectron impact ionization of the medium sets in to create low-densityplasma in the high intensity portion of the laser beam. This plasmatemporarily lowers the refractive index in the centre of the beam pathcausing the beam to defocus and break up the filament. The dynamicbalance between Kerr effect self-focusing and plasma defocusing can leadto multiple re-focused laser interaction filaments through to formationof a stable filament, sometimes called a plasma channel. As show in theexamples below, using picosecond pulses, the present inventors havefound that when the pulse focuses, it stays confined for about 500 to1000 μm (depending on the focusing lens which is used), and thenspatially diverges when there is no more material for refocusing andforming the next filament, or when the pulses do not have enough energyto refocus to form another plasma channel.

Optical breakdown, on the other hand, is the result of a tightly focusedlaser beam inside a transparent medium that forms a localized denseplasma around the geometrical focus. The plasma generation mechanism isbased on initial multi-photon excitation of electrons, followed byinverse Bremsstrahlung, impact ionization, and electron avalancheprocesses. Such processes underscore the refractive index and voidformation processes described above [U.S. Pat. No. 6,154,593; SPIEProceedings 6881-46,], and form the basis of most short-pulse laserapplications for material processing. In this optical breakdown domain,the singulation, dicing, scribing, cleaving, cutting, and facettreatment of transparent materials has disadvantages such as slowprocessing speed, generation of cracks, contamination by ablationdebris, and large kerf width.

In contrast, laser filamentation offers a new direction for internallaser processing of transparent materials that can avoid ablation orsurface damage, dramatically reduce kerf width, avoid crack generation,and speed processing times for such scribing applications. Further, highrepetition rate lasers defines a new direction to enhance the formationof laser beam filaments with heat accumulation and other transientresponses of the material on time scales faster than thermal diffusionout of the focal volume (typically <10 microseconds).

Accordingly, embodiments disclosed herein harnesses short duration laserpulses (preferably with a pulse duration less than about 100 ps) togenerate a filament inside a transparent medium. The method avoids denseplasma generation such as through optical break down that can be easilyproduced in tight optical focusing conditions as typically applied andused in femtosecond laser machining. In weak focusing, which ispreferential, the nonlinear Kerr effect is believed to create anextended laser interaction focal volume that greatly exceeds theconventional depth of focus, overcoming the optical diffraction thatnormally diverges the beam from the small self-focused beam waist.

Once a filamentation array is formed in the transparent substrate, onlysmall mechanical pressure is required to cleave the substrate into twoparts on a surface shape that is precisely defined by the internallaser-filamentation curtain. The laser-scribed facets typically show noor little cracking and microvoids or channels are not evident along thescribed zone. There is substantially no debris generated on the top orbottom surfaces since laser ablation at the surfaces can be avoided byconfining the laser filament solely within the bulk glass. On the otherhand, simple changes to the laser exposure or sample focusing conditionscan move the filament to the surface and thus induce laser ablationmachining if desired, as described further below. This assists increating very sharp V groves on the surface of the substrate. To scribevery thin substrates (less than 400 um thick) creating a sharp V grooveis desired. Other common ablation techniques generally create U groovesor rounded V grooves. V grooves also can form on both top and bottomsurface of the sample making scribed edges chamfered.

Laser energy deposited along such filaments leads to internal materialmodification that can be in the form of defects, color centers, stress,microchannels, microvoids, and/or microcracks. The present methodentails lateral translation of the focused laser beam to form an arrayof closely positioned filament-induced modification tracks. Thisfilament array defines a pseudo-continuous curtain of modificationinside the transparent medium without generating laser ablation damageat either of the top or bottom surfaces. This curtain renders the glassplate highly susceptible to cleaving when only very slight pressure(force) is applied, or may spontaneously cleave under internal stress.The cleaved facets are devoid of ablation debris, show minimal or nomicrocracks and microvents, and accurately follow the flexiblecurvilinear or straight path marked internally by the laser with onlyvery small kerf width as defined by the self-focused beam waist.

The application of high repetition rate bursts of short-pulse lasersoffers the advantage of heat accumulation and other transient effectssuch that thermal transport and other related mechanisms are not fullyrelaxed prior to the arrival of subsequent laser pulses [U.S. Pat. No.6,552,301 B2 Burst-UF laser Machining]. In this way, heat accumulation,for example, can present a thin heated sheath of ductile glass tosubsequent laser pulses that prevents the seeding of microcracks whilealso retaining the advantages (i.e. nonlinear absorption, reducedcollateral damage) of short pulse ablative machining in an otherwisebrittle material. In all the above laser ablation methods, the cutting,scribing, or dicing of transparent materials will generate ablationdebris contamination and consume a kerf width to accommodate the removedmaterial, while also generating collateral laser damage. Therefore, anon-ablative method of laser processing would be desirable.

The application of high repetition rate short-pulse lasers thus offers ameans for dramatically increasing the processing (scan) speed for suchfilamentation cleaving. However, at sufficiently high repetition rate(transition around 100 MHz to 1 MHz), the modification dynamics of thefilament is dramatically enhanced through a combination of transienteffects involving one or more of heat accumulation, plasma dynamics,temporary and permanent defects, color centers, stresses, and materialdefects that accumulate and do not relax fully during the train ofpulses to modify the sequential pulse-to-pulse interactions. Laserfilaments formed by such burst trains offer significant advantage inlowering the energy threshold for filament formation, increasing thefilament length to hundreds of microns or several millimeters, thermallyannealing of the filament modification zone to minimize collateraldamage, improving process reproducibility, and increasing the processingspeed compared with the use of low repetition rate lasers. In onenon-limiting manifestation at such high repetition rate, there isinsufficient time (i.e. 10 nsec to 1 μs) between laser pulses forthermal diffusion to remove the absorbed laser energy, and heat therebyaccumulates locally with each laser pulse. In this way, the temperaturein the interaction volume rises during subsequent laser pulses, leadingto laser interactions with more efficient heating and less thermalcycling. In this domain, brittle materials become more ductile tomitigate crack formation. Other transient effects include temporarydefects and plasma that survive from previous laser pulse interactions.These transient effects then serve to extend the filamentation processto long interaction lengths, and/or improve absorption of laser energyin subsequent pulses.

As shown below, the laser filamentation method can be tuned by variousmethods to generate multi-filament tracks broken with non-filamentingzones through repeated cycles of Kerr-lens focusing and plasmadefocusing. Such multi-level tracks can be formed in a thick transparentsample, across several layers of glasses separated by transparent gas orother transparent materials, or in multiple layers of differenttransparent materials. By controlling the laser exposure to only formfilaments in the solid transparent layers, one can avoid ablation anddebris generation on each of the surfaces in the single or multi-layerplates. This offers significant advantages in manufacturing, forexample, where thick glasses or delicate multilayer transparent platesmust be cleaved with smooth and crack free facets.

The filamentation method applies to a wide range of materials that aretransparent to the incident laser beam, including glasses, crystals,selected ceramics, polymers, liquid-encapsulated devices, multi-layermaterials or devices, and assemblies of composite materials. In thepresent disclosure, it is further to be understood that the spectralrange of the incident laser beam is not limited to the visible spectrum,but represents any material that is transparent to a laser wavelengthalso in the vacuum ultraviolet, ultraviolet, visible, near-infrared, orinfrared spectra. For example, silicon is transparent to 1500 nm lightbut opaque to visible light. Thus, laser filaments may be formed insilicon with short pulse laser light generated at this 1500 nmwavelength either directly (i.e. Erbium-doped glass lasers) or bynonlinear mixing (i.e. optical parametric amplification) in crystals orother nonlinear medium.

In substrates that are transparent within the visible spectrum, thelaser filament may result in the generation of white light, whichwithout being limited by theory, is believed to be generated by selfphase modulation in the substrate and observed to emerge for the laserfilamentation zone in a wide cone angle 16 after the filament ends dueto factors such reduced laser pulse energy or plasma defocusing.

The length and position of the filament is readily controlled by thelens focusing position, the numerical aperture of objective lens, thelaser pulse energy, wavelength, duration and repetition rate, the numberof laser pulses applied to form each filament track, and the optical andthermo-physical properties of the transparent medium. Collectively,these exposure conditions can be manipulated to create sufficiently longand strong filaments to nearly extend over the full thickness of thesample and end without breaking into the top or bottom surfaces. In thisway, surface ablation and debris can be avoided at both surfaces andonly the interior of the transparent substrate is thus modified. Withappropriate beam focusing, the laser filament can terminate and causethe laser beam to exit the glass bottom surface at high divergence angle16 such that laser machining or damage is avoided at the bottom surfaceof the transparent plate.

FIG. 2 presents a schematic arrangement shown in a side view for (a)forming laser filaments 20 with surface V groove formation 22(b) Vgroove formation with suppressed filament formation. For higher qualityscribing with edge chamfered property, laser processing can be arrangedsuch that filaments forms inside the transparent material and very sharpV groove that is the result of ablation from on top of the surface. Forsome applications where clean facet is required or higher scribing speedis considered, filaments can be suppressed or completely removed.

In one embodiment, the method is employed for the scribing and cleavingof optical display glass substrates such as flat panel displays. A flatpanel display is the sandwich of two glasses substrates. The bottomglass substrate may be printed with circuits, pixels, connectors, and/ortransistors, among other electrical elements. A gap between thesubstrates is filled with liquid crystal materials. The top and leftedge of the LCD can be scribed without any offset but the right andbottom edge typically has an offset of about 5 mm which is call the padarea, and all electronics connected through this region to the LCDelements.

This area is the source of a major bottleneck that limits using highpower lasers for flat panel display laser scribing, because during toplayer scribing, all the circuitry on the bottom layer may be damaged. Tosimulate a flat panel device, the inventors placed a top glass substrateon the surface of a coated mirror. During laser filament scribing of thetop glass of a double glass plate, it is preferably to adjust thelocation of filaments formed within the top glass plate so as to avoiddamage on the bottom layer that generally contains a metal coating (asdescribed above). The results from this experiment highlighted twoimportant points. Firstly, laser scribing can be achieved withoutdamaging the coating of the bottom substrate pad area, and secondly,when filaments located in a special position closer to the bottomsurface, reflection from the bottom metal surface may machine or processthe bottom surface of the top layer, creating a V groove on the bottom.

Further investigation results in the method illustrated in FIG. 3, wherethe diffracted beam 16 is converged back by means of proper concavemirror 24 or combination of mirror and lens to machine the bottomsurface of the target to produce second V groove 26. The apparatus hasthe benefit of making V groove in the bottom edge without using secondlaser machining from bottom side.

For some applications where a clean or shiny facet is required, thearrangement of FIG. 4 may be employed to create sharp V grooves on thetop and bottom layer of the glass. In this mode of operation both edgesare chamfered through laser scribing via the addition of a second beam28 and objective 30, and no need for further chamfering or grinding thatwould otherwise necessitate washing and drying. The side and front viewof the cleaved sample is shown in FIG. 5, where the surface of V groove32 is shown after cleaving.

FIG. 6 presents an example of a focusing arrangement for deliveringmultiple converging laser beams into a transparent plate for creatingmultiple filaments simultaneously. The beams 10 and 34 maybe separatedfrom a single laser source using well know beam splitter devices andfocused with separate lenses 12 and 36 as shown. Alternatively,diffractive optics, multi-lens systems and hybrid beam splitting andfocusing systems may be employed in arrangements well known to anoptical practitioner to create the multiple converging beams that enterthe plate at different physical positions, directions, angles, anddepths. In this way, filamentation modification tracks 18 are created inparallel in straight or curvilinear paths such that multiple parts ofthe plate can be laser written at the same time and subsequently scribedalong the multiple modification tracks for higher overall processingspeed.

FIG. 7 presents a schematic arrangement for two different focusingconditions for laser filamentation writing that confines the array 38 ofmodification tracks 40 solely in a top transparent substrate 42 (FIG. 7(a)) as a first laser exposure step, and followed sequentially byfilamentation writing that solely confines the array 44 of modificationtracks 46 inside a lower transparent plate 48 (FIG. 7( b)) in a secondlaser pass. The laser exposure is tuned to avoid ablation or other laserdamage and generation of ablation debris on any of the four surfacesduring each laser pass. During scribing of the top plate, no damageoccurs in the bottom layer, and visa versa.

One advantage of this one-sided processing is that the assembly oftransparent plates does not need to be flipped over to access the secondplate 48 due to the transparency of the first plate to the converginglaser beam 50. For example, by position the 12 lens closer to the topglass plate 42 in the second pass (FIG. 7 b), the filamentation is notinitiated in the first plate and near full laser energy enters thesecond plate where filamentation is then initiated. A second advantageof this approach is that the two plates can be separated along similarlines during the same scribing step which is attractive particularly forassembled transparent plates in flat panel display. This method isextensible to multiple transparent plates.

FIG. 7( c) shows an arrangement for inducing laser filamentationsimultaneously in two or more transparent plates 42 and 48. This methodenables a single pass exposure of both transparent plates to formnear-identical shapes or paths of the filamentation modification tracks38 and 44. In this case, laser parameters are adjusted to create a firstfilament 38 or array of filament tracks 40 within the top plate 42, suchthat the filamentation terminates prior to reaching the bottom surfaceof the top plate, for example, by plasma de-focusing. The diverginglaser beam is sufficiently expanded after forming the first filamenttrack to prevent ablation, optical breakdown, or other damage to bottomsurface of the top plate, the medium between the two plates, and the topsurface of the bottom plate 48.

However, during propagation in this region, self focusing persists andresults in the creation of a second filament 44 that is confined solelyin the bottom layer transparent plate 48. As such, a single laser beamsimultaneously forms two or more separated filaments 38 and 44 thatcreate parallel modification tracks 40 and 46 in two or more stackedplates at the same time. In this way, an assembly of two or moretransparent plates can by scribed or separated along the near-parallelfilamentation tracks and through all transparent plates in one cleavingstep. The medium between the transparent plates must have goodtransparency and may consist of air, gas vacuum, liquid, solid orcombination thereof. Alternatively, the transparent plates may be inphysical or near-physical contact without any spacing. This method isextensible to filament processing in multiply stacked transparentplates.

FIG. 8 provides another embodiment of the multibeam filamentationscribing method (shown initially in FIG. 4) for processing double ormultiple stacked or layer transparent plates and assemblies. Twoconverging laser beams are presented to the plate assembly 42 and 48 forcreating independent and isolated filaments 38 and 44 in physicallyseparated or contacted transparent plates. Laser exposure conditions areadjusted for each laser beam 10 and 28 (i.e. by vertical displacement oflenses 12 and 30) to localize the filament in each plate. The filamenttracks are then formed in similar or off-set positions with similar ordifferent angles and depths. The filamentation tracks may be cleavedsimultaneously such that the stack or assembly of optical plates isseparated as one unit in a batch process. The upper and lower beams maybe provided from a common optical source using conventional beamsplitter or may original from two different laser sources. The upper andlower beams may be aligned along a common axis, or spatially offset.Preferably, the relative spatial positioning of the two beams isconfigurable.

FIG. 9( a) illustrates a method of processing double layer glass (formedfrom plates 42 and 48) in which each layer is processed in twolocations, but where one pair of filaments 52 and 54 is aligned andanother pair of filaments 56 and 58 are offset laterally from eachother. Such an arrangement can be obtained by using the methodillustrated in FIG. 8, where each plate is processed by a separate laserbeam. Alternatively, the filaments may be processed using one of themethods illustrated in FIG. 7.

FIG. 9( b) shows a similar arrangement in which a filament is formed inboth the upper 42 and 48 plates with groove formation (60, 62, 64 and66) on the top of each glass, where the method illustrated in FIG. 7 ispreferably employed. Similarly, FIG. 9( c) illustrates a case where onlyV grooves 68, 70, 72 and 74 are developed on the surface of each plate42 and 48. Note that V groove or filament for the bottom glass can beformed in bottom surface using similar apparatus as shown in FIG. 4 andFIG. 8.

In the context of flat panel displays, it is to be noted that providinga V groove on the top surface of the bottom layer requires the machiningof extra connections in the pad area. Furthermore, due to shadow effectof connections, filaments don't form in all places. Nonetheless, thesubstrate may be cleaved with relative easy without perfect facet view.In some cases, edges may be improved by grinding.

FIG. 10 shows the resulting formation of filaments and V-grooves indouble layer glass after scribing using the method as shown in FIG. 8.As described above, the upper plate is scribed from the top and thelower plate is scribed from bottom, where V-grooves 76 and 78 areformed. A V groove, a filament, or a combination thereof (as shown inthe Figure) may be formed. As shown, upper and lower filaments may beoffset, where the filament 56 and V grove 64 in the upper plate isspatially offset relative to the filament 58 and V groove 78 in thelower plate. Alternatively, upper and lower filaments may be aligned,where the filament 52 and V grove 60 in the upper plate is spatiallyaligned with filament 54 and V groove 76 in the lower plate. In such aconfiguration, forming a filament and V groove readily achievable inthis configuration, and the scribed regions are efficiently separatedduring cleaving. Generally speaking, cleaving of top layer is occurswith relative ease, but the inventors have determined that in somecases, the bottom layer warrants careful attention and it may benecessary to properly adjust a cleaving roller prior to the cleavingstep. Those skilled in the art will readily appreciate that adjustmentmay be made by selecting a roller configuration that yields the desiredcleave quality.

New approaches in photonics industry involve assemblies of multiplelayers of transparent plates that form a stack. For example, touchscreen LCDs and 3D LCDs employ three layers of glass. The parallelprocessing of such a multi-layer stack 80 is shown in FIG. 11, where thescribe line 82 is shown as being provided to each plate in the stack. Asshown in FIGS. 7( a) and 7(b), multiple plates in such a stack may beprocessed by varying the working distance of the objective 12, whichenables multiple plates within the stack to be individually scribed.Scribing can be done from both surfaces (similar to the method shown inFIG. 7). Only a top focusing apparatus is shown in the specific caseprovided here.

The following examples are presented to enable those skilled in the artto understand and to practice the present disclosure. They should not beconsidered as a limitation on the scope of the embodiments providedherein, but merely as being illustrative and representative thereof.

EXAMPLES

To demonstrate selected embodiments, a glass plate was laser processedusing a pulsed laser system with an effective wavelength of about 800nm, producing 100 fs pulses at a repetition rate of 38 MHz. The laserwavelength was selected to be within the infrared spectral region, wherethe glass plate is transparent. Focusing optics were selected to providea beam focus of approximately 10 μm. Initially, the laser system wasconfigured to apply a pulse train of 8 pulses, where the burst of pulsesforming the pulse train occurred at a repetition rate of 500 Hz. Variousconfigurations of aforementioned embodiments were employed, as describedfurther below.

FIGS. 12( a)-(c) shows microscope images in a side view of 1 mm thickglass plates viewed through a polished edge facet immediately afterlaser exposure. The plate was not separated along the filament track forthis case in order to view the internal filament structure. As notedabove, a single burst of 8 pulses at 38 MHz repetition rate was appliedto form each filament track. Furthermore, the burst train was presentedat 500 Hz repetition rate while scanning the sample at a moderate speedof 5 mm/s, such that filament tracks were separated into individualtracks with a 10 μm period. The filamentation modification tracks wereobserved to have a diameter of less than about 3 μm, which is less thanthe theoretical focal spot size of 10 μm for this focusing arrangement,evidencing the nonlinear self focusing process giving rise to theobserved filamentation.

The geometric focus of the laser beam in the sample was varied by thelens-to-sample displacement to illustrate the control over the formationof the filaments within the sample. In FIG. 12( a), the beam focus waspositioned near the bottom of the plate, while in FIGS. 12( b) and12(c), the beam focus was located near the middle and top of the plate,respectively. FIGS. 12( a) and 12(b) show multiple layers of filamenttracks (84, 86, 88 and 90) formed through the inside of the glass plate.Notably, the filaments are produced at multiple depths due to defocusingand re-focusing effects as described above.

FIG. 12 thus demonstrates the controlled positioning of thefilamentation tracks relative to the surfaces of the plate. In FIG. 12(a), where the beam focus was located near the bottom of the plate, thefilaments were formed in the top half of the plate and do not extendacross the full thickness of the plate. In FIG. 12( c), where the beamfocus was positioned near the top of the plate, relative short filaments92 of approximately 200 μm are formed in the center of the plate, andtop surface ablation and ablation debris are evident. A preferably formfor scribing is depicted in FIG. 12( b) where approximately 750 μm longbands of filaments extend through most of the transparent platethickness without reaching the surfaces. In this domain, ablativemachining or other damage was not generated at both of these surfaces.

While the spacing of the filament tracks in FIG. 12 is sufficient tocleave the thick 1 mm glass plate, it was found that moderately highmechanical force was required to cleave the plate along the desired pathdefined by the filament array. In several tests, it was observed thatthe glass occasionally cleaved to outside the laser modification track.Therefore, a closer spacing of the filament tracks (i.e. a smaller arraypitch) is preferable for cleaving such thick (1 mm) plates.

Those skilled in the art will readily appreciate that suitable valuesfor the array spacing and filament depth will depend on the materialtype and size of a given plate. For example, two plates of equalthickness but different material composition may have different suitablevalues for the array spacing and filament depth. Selection of suitablevalues for a given plate material and thickness may be achieved byvarying the array spacing and filament depth to obtain a desired cleavequality and required cleave force.

Referring again to FIG. 12, since the array pitch is 10 μm and theobserved filament diameter is approximately 3 microns, only a narrowregion is heat affected compared with theoretical laser spot size of 10μm. In other laser material processing methods, obtaining a small heataffected zone is a challenge. One specific advantage of the presentmethod, as evidenced by the results shown in FIG. 12, is that the widthof the heat affected zone on the top and bottom surfaces look theapproximately the same. This is an important characteristic of thepresent method, since the filamentation properties remain substantiallyconfined during formation, which is desirable for accurately cleaving aplate.

FIGS. 13( a) and 13(b) presents optical microscope images focusedrespectively on the top and bottom surface of the glass sample, asrecorded for the sample shown in FIG. 12( b). In between these surfaces,the internal filamentation modification appears unfocused as expectedwhen the modification zone is physically more than 100 μm from eithersurface due to the limited focal depth of the microscope. The imagesreveal the complete absence of laser ablation, physical damage or othermodification at each of the surfaces while only supporting the internalformation of along laser modification track.

The width of the filamentation modification zone was observed to beabout 10 μm when the microscope was focused internally within the glass.This width exceeds the 3-μm modification diameter seen in FIG. 12 forisolated laser filaments and is ascribed to differing zones of narrowhigh contrast filament tracks (visible in FIG. 12) that have beenshrouded in a lower contrast modification zone (not visible in FIG. 12).Without intending to be limited by theory, this low contrast zone thatis ascribed to an accumulative modification process (i.e. heat affectedzone) is induced by the multiple pulses in the burst.

The filamentation modification zone maintains a near constant 10 μmwidth through its full depth range of hundred's of microns in thepresent glass sample that clearly demonstrates the self-focusingphenomenon. Thus, the filamentation modification presents a 10 μm‘internal’ kerf width or heat affected zone for such processing.However, the absence of damage or physical changes at the surfaceindicate that a much smaller or near-zero kerf width is practicallyavailable at the surface where one typically only finds other componentsmounted (paint, electronics, electrodes, packaging, electro-optics,MEMS, sensors, actuators, microfluidics, etc.). Hence, a near-zero kerfwidth at the surface of transparent substrates or wafers is asignificant processing advantage to avoid damage or modification to suchcomponents during laser processing. This is one of the importantproperties of the present disclosure for laser filamentation scribing asthe physical modification may be confined inside the bulk transparentmedium and away from sensitive components or coatings.

To facility cleaving, laser exposure conditions as presented for FIG.12( b) were applied to a similar 1 mm thick glass sample while using aslower scanning speed to more closely or densely space the filamenttracks. Individual filament tracks were no longer resolvable by opticalmicroscopy. FIG. 14( a) shows the end facet view after the sample wasmechanically cleaved along the near continuous laser-formedfilamentation plane. Under these conditions, only very slight force orpressure is required to induce a mechanical cleave. The cleaveaccurately follows the filament track and readily propagates the fulllength of the track to separate the sample. The resulting facet is veryflat and with sharply defined edges that are free of debris, chips, andvents.

The optical morphology shows smooth cleavage surfaces interdispersedwith rippled structures having feature sizes of tens of microns that aregenerally smooth and absent of cracks. The smooth facet regionscorrespond to regions where little or no filamentation tracks wereobservable in views such as shown in FIG. 12. Sharply defined top andbottom surface edges may be obtained by controlling the laser exposureto confine the filament formation entirely within the glass plate andprevent ablation at the surfaces. The laser filamentation interactionhere generates high stress gradients that form along an internal planeor surface shape defined by the laser exposure path. This stress fieldenables a new means for accurately scribing transparent media in pathscontrolled by the laser exposure.

FIG. 14( b) presents a side view optical image of the 1 mm thick glasssample shown in FIG. 12( b) after cleaving. Due to the faster scan speedapplied during this laser exposure, less over stress was generated dueto the coarse filament spacing (10 μm). As a result, more mechanicalforce was necessary to separate the plate. The cleaved facet nowincludes microcracks, vents, and more jagged or coarse morphology thanas seen for the case in FIG. 14( a) with slower scanning speed. Suchmicrocracks are less desirable in many applications as the microcracksmay seed much large cracks under packaging or subsequent processingsteps, or by thermal cycling in the application field that canprematurely damage the operation or lifetime of the device.

The laser filamentation and scribing examples presented in FIGS. 12-14for glass clearly demonstrate the aforementioned embodiments in ahigh-repetition rate method of forming filaments with short pulseslasers is employed. Each filament was formed with a single burst of 8pulses, with pulses separated by 26 ns and with each pulse having 40-μJenergy. Under such burst conditions, heat accumulation and othertransient effects do not dissipate in the short time between pulses,thus enhancing the interaction of subsequent laser pulses with in thefilamentation column (plasma channel) of the prior pulse. As such,filaments were formed much more easily, over much longer lengths, andwith lower pulse energy, higher reproducibility and improved controlthan for the case when laser pulses were applied at low repetition rate.

FIG. 15( a) shows a microscope image of a cleaved glass plate of 1 mmthickness in which filaments were formed at a low 500 Hz repetition rate(2 ms between laser pulses). The scanning rate was adjusted to deliver 8pulses per interaction site with each pulse having the same 40 μJ pulseenergy as used in the above burst-train examples. The total exposure persingle filament was therefore 320 μJ in both cases of burst (FIGS.12-14) and non-burst (FIG. 15) beam delivery. The long time separationbetween pulses in the non-burst case (FIG. 15( a)) ensures relaxation ofall the material modification dynamics prior to the arrival of the nextlaser pulse. This precludes any filamentation enhancement effect as heataccumulation and other transient effects are fully relaxed in the longinterval between pulses.

Without intending to be limited by theory, the relaxation of materialmodification dynamics are believed to lead to much weaker overalllaser-material interaction in creating filaments and inducing internalmodification within the present glass substrate. As a consequence,non-burst laser interactions take place in a very small volume that isnear the top glass surface as shown in FIG. 15( a). Further, laserinteractions produced small volume cavities inside the glass that canseen in FIG. 15( a) as the rough surface in the top 100 μm of the facet.In order to enable reliable scribing along such laser tracks, it isnecessary to pass the laser much more slowly (than the case in FIG. 15(a)) through the sample and/or to apply several repeated passes of thelaser over the same track to build up sufficiently strong internalmodification.

For direct comparison with burst-train filament writing, FIG. 15( b)shows an edge facet image of a similar glass plate in which filamentswere each formed in the low-repetition rate of 500 Hz at 320 μJ energyper pulse (i.e. 320 μJ for burst train: single pulse in the train). Muchlonger filaments (˜180 μm) than in the low-repetition rate 8-pulseexposure of FIG. 15( a) is observed. The filaments are deeply buriedwithin the bulk glass so too avoid surface ablation or other laserdamage. Nonetheless, the observed filament length is smaller than thatobserved for burst filamentation at a similar mean fluence. In bothcases of FIGS. 15( a) and 15(b), a common rapid scan speed was appliedto provide a broad spacing of the filament array for observationalpurposes.

Accordingly, these results illustrate that the nature of the filamentcan be readily manipulated by varying the pulsed nature of the laserexposure. In other words, in addition to the parameters of energy,wavelength, and beam focusing conditions (i.e. numerical aperture, focalposition in sample), pulse parameters can be tailored to obtain adesired filament profile. In particular, number of pulses in a pulseburst and the delay time between successive pulses can be varied tocontrol the form of the filaments produced. As noted above, in oneembodiment, filaments are produced by providing a burst of pulses forgenerating each filament, where each burst comprises a series of pulsesprovided with a relative delay that is less than the timescale for therelaxation of all the material modification dynamics.

In the industrial application of single sheet glass scribing, flat panelglass scribing, silicon and/or sapphire wafer scribing, there is ademand for higher scribing speeds using laser systems with provenreliability. To demonstrate such an embodiment, experiments wereperformed using a high repetition rate commercial ultrafast laser systemhaving a pulse duration in the picosecond range.

As shown in FIG. 16( a), a V groove with a filament descending from theV groove was produced in a glass substrate having a thickness of 700microns. The depth and width of the V is about 20 μm and the filamentextended to a length of about 600 μm. FIG. 16( b) provides a top view ofthe glass substrate. The observed kerf width is about 20 μm, coveredwith about 5 μm recast in the sides. As shown in the Figure, no visibledebris is accumulated on the surface. FIG. 16( c) shows a front view ofthe glass after it is cleaved, highlighting the deep penetration of thefilaments into the glass substrate that assist in cleaving the sample.

In a subsequent experiment, the focusing condition was changed tominimize the filament length. For some applications, filament formationis not desired, and/or a clean facet is desirable. A side view showingthree different V grooves is provided in FIG. 17. Note that the chamferangle is different for each V. The chamfer angle and depth can beadjusted by changing the focus and beam divergence. The width, depth andsharpness of the V grooves are of high quality comparing to other laserscribing techniques where they generally create wider kerf width orshorter depth structures with grooves having a U-shaped and causing alarge amount of debris to accumulate on the surface.

FIG. 18 presents the simultaneous laser filamentation scribing of anassembly of two 400 um thick double layer glasses by the method andarrangement described by FIG. 7( c). A single laser beam was focusedinto the top glass plate to form a long filament. The laser beam passedthrough the air gap without creating damage to the two middle glasssurfaces. However, self-focusing effects created a second filament toform with the same beam in the second (lower) plate such that twofilament tracks were formed separately in each thin glass plate.

FIG. 18( a) shows a side view of the scribed laminated glass beforecleaving and FIG. 18( b) shows optical microscope images of the frontsurfaces of top and bottom layer glasses after cleaving. Themodification tracks are largely confined with in the bulk of the glass,and thus, no ablation debris or microcracks are present in any of thesurfaces. The kerf width of the filamentation modification is less than10 μm in both plates which represents the heat affect zone of the laser.Individual filament tracks are resolvable around which internal stressfields were generated that enabled the mechanical scribing. The facethas clean flat surfaces with only a small degree of contouring aroundthe filament tracks observable. The edges are relatively sharp andabsent of microcracks. The facet has the general appearance of a grindedsurface, and may be referred to as having been produced by “lasergrinding”. Such clean and “laser grinded” surfaces may be obtained bycreating filaments that are tightly spaced, and preferably, adjacent toeach other.

It is to be noted that for each of the optical microscope images inFIGS. 12 to 18, the glass samples are presented as processed by laserexposure without any cleaning steps following the laser exposure orafter the cleaving steps.

The present method of low and high (burst) repetition rate filamentationwas found to be effective in glass for pulse durations tested in therange of about 30 fs to 10 ps. However, those skilled in the art willappreciate that the preferably pulse duration range for other materialsmay be different. Those skilled in the art may determine a suitablepulse duration for other materials by varying the pulse duration andexamining the characteristics of the filaments produced.

Without intending to be limited by theory, it is believe thatembodiments as disclosed herein utilize self-focusing to generatefilaments (plasma channels) in transparent materials. Therefore, laserpulse durations in the range of 1 femtosecond to 100 ps are consideredthe practical operating domain of the present disclosure for generatingappropriately high intensity to drive Kerr-lens self focusing in mosttransparent media.

The present disclosure also anticipates the formation of thermalgradients in the transparent substrate through non-uniform heating bythe focused short duration laser light. Such effects may be enhanced byheat accumulation effects when burst-trains of pulses are applied. Inthis domain, thermal lensing serves as an alternate means for generatinga filament or long-focusing channel to produce filament modificationtracks in transparent materials for scribing application.

The filamentation modification of transparent media enables rapid andlow-damage singulation, dicing, scribing, cleaving, cutting, and facettreatment of transparent materials that are typically in the form of aflat or curved plate, and thus serve in numerous manufacturingapplications. The method generally applies to any transparent medium inwhich a filament may form. For glass materials, this includes dicing orcleaving of liquid crystal display (LCD), flat panel display (FPD),organic display (OLED), glass plates, multilayer thin glass plates,autoglass, tubing, windows, biochips, optical sensors, planar lightwavecircuits, optical fibers, drinking glass ware, and art work. Forcrystals such as silicon, III-V, and other semiconductor materials,particularly, those in thin wafer form, applications include singulationof microelectronic chips, memory chips, sensor chips, light emittingdiodes (LED), laser diodes (LD), vertical cavity surface emitting laser(VCSEL) and other optoelectronic devices. This filament process willalso apply to dicing, cutting, drilling or scribing of transparentceramics, polymers, transparent conductors (i.e. ITO), wide bandgapglasses and crystals (such as crystal quartz, diamond, sapphire). Theapplications also extend to all composite materials and assemblies wereat least one material component is transparent to the laser wavelengthto facilitate such filamentation processing. Examples include silica onsilicon, silicon on glass, metal-coated glass panel display, printedcircuit boards, microelectronic chips, optical circuits, multi-layer FPDor LCD, biochips, sensors, actuators, MEMs, micro Total Analysis Systems(μTAS), and multi-layered polymer packaging.

The specific embodiments described above have been shown by way ofexample, and it should be understood that these embodiments may besusceptible to various modifications and alternative forms. It should befurther understood that the claims are not intended to be limited to theparticular forms disclosed, but rather to cover all modifications,equivalents, and alternatives falling within the spirit and scope ofthis disclosure.

1. A method of preparing a substrate for cleavage, the method comprisingthe steps of: irradiating the substrate with a burst of pulses of afocused laser beam, wherein the substrate is transparent to the focusedlaser beam, wherein a time delay between successive pulses in the burstof pulses is less than a time duration over which relaxation of one ormore material modification dynamics occurs, and wherein the burst ofpulses have an energy and pulse duration selected to produce a filamentwithin the substrate; translating the substrate relative to the focusedlaser beam to irradiate the substrate and produce an additional filamentat one or more additional locations; wherein the filaments form an arraydefining an internally scribed path for cleaving the substrate.
 2. Themethod according to claim 1 wherein substrate is translated relative tothe focused laser beam with a rate selected to produce a filamentspacing on a micron scale.
 3. The method according to claim 1 whereinthe burst of pulses are provided two or more times with a prescribedfrequency, and wherein the substrate is translated relative to thefocused laser beam with a substantially constant rate.
 4. (canceled) 5.(canceled)
 6. (canceled)
 7. The method according to claim 1 wherein alocation of a beam focus of the focused laser beam is selected togenerate the filaments within the substrate, wherein at least onesurface of the substrate is substantially free from ablation.
 8. Themethod according to claim 1 wherein properties of the burst of pulsesare selected to provide a sufficient beam intensity within the substrateto cause self-focusing of the focused laser beam and substantiallyuniform modification of the material along the beam path.
 9. The methodaccording to claim 1 wherein a location of a beam focus of the focusedlaser beam is selected to generate a V groove within at least onesurface of the substrate.
 10. The method according to claim 1 whereinthe substrate is a glass.
 11. The method according to claim 1 whereinthe substrate includes a semiconductor.
 12. The method according toclaim 1 wherein the substrate is selected from the group consisting oftransparent ceramics, polymers, transparent conductors, wide bandgapglasses, crystals, crystal quartz, diamond, and sapphire.
 13. The methodaccording to claim 1 wherein the substrate includes a first layer andone or more additional layers, and wherein a location of a beam focus ofthe focused laser beam is selected to generate filaments within at leastone of the one or more additional layers.
 14. The method according toclaim 13 wherein the substrate includes multi-layer flat panel displayglass.
 15. The method according to claim 14 wherein the flat paneldisplay glass is selected from the group consisting of liquid crystaldisplay (LCD), flat panel display (FPD), and organic light emittingdisplay (OLED).
 16. The method according to claim 13 wherein thesubstrate is selected from the group consisting of auto glass, tubing,windows, biochips, optical sensors, planar lightwave circuits, opticalfibers, drinking glass ware, art glass, silicon, III-V semiconductors,microelectronic chips, memory chips, sensor chips, light emitting diodes(LED), laser diodes (LD), and vertical cavity surface emitting laser(VCSEL).
 17. The method according to claim 13, wherein the location ofthe beam focus of the focused laser beam is selected to generatefilaments within two or more layers, wherein the focused laser beamgenerates a first filament in one layer, propagates into at least one ofthe one or more additional layers, and generates a second filament inthe at least one of the one or more additional layers.
 18. The methodaccording to claim 1 further comprising the step of cleaving thesubstrate.
 19. The method according to claim 1 wherein a pulse durationof each pulse is less than about 100 ps.
 20. The method according toclaim 1 wherein a pulse duration of each pulse is less than about 10 ps.21. The method according to claim 13 wherein the location of the beamfocus of the focused laser beam is first selected to generate filamentswithin the first layer, the method further comprising the steps of:positioning a second beam focus within a second layer, wherein thesecond layer is one of the one or more additional layers; andirradiating the second layer and translating the substrate to produce asecond array of filaments defining a second internally scribed path forcleaving the substrate.
 22. The method according to claim 21 whereinwhen irradiating the second layer, the substrate is irradiated from anopposite side relative to when irradiating the first layer.
 23. Themethod according to claim 21 wherein prior to irradiating the secondlayer, a position of the second beam focus is laterally translated toproduce an offset relative to a first position of a first beam focuswhen irradiating the first layer.
 24. The method according to claim 21wherein a second focused laser beam is used to irradiate the secondlayer.
 25. The method according to claim 1 wherein the pitch of thearray is less than or equal to approximately 10 microns.
 26. The methodaccording to claim 1 wherein a length of the filaments exceedsapproximately 250 microns.
 27. The method according to claim 1 wherein alength of the filaments exceeds approximately 600 microns.
 28. Themethod according to claim 1 wherein a diameter of the filament is lessthan approximately 3 microns.
 29. The method according to claim 1wherein a diameter of the filament is less than approximately 10microns.
 30. The method according to claim 1 wherein, upon cleavage ofthe substrate, the kerf width is less than approximately 30 microns. 31.The method according to claim 1 wherein the filaments extend over asubstantial portion of the substrate.
 32. The method according to claim31 wherein the filaments end without breaking into top or bottomsurfaces of the substrate.
 33. The method according to claim 31 whereina location of a beam focus of the focused laser beam is selected togenerate a V groove within at least one surface of the substrate. 34.The method according to claim 1 wherein a diffracted beam emergingthrough a bottom surface of the substrate is converged back onto thebottom surface of the substrate by a focusing element, such that a Vgroove is produced in the bottom surface of the substrate.
 35. Themethod according to claim 1 wherein upon cleaving the substrate, theedge of the cleaved substrate is substantially free of chipping andmicrocracks.